1. Field of the Invention
The present invention relates to an evacuation system used in, for example, evacuating a processing chamber of a semiconductor fabrication apparatus.
2. Description of the Related Art
A conventional evacuation system will be explained with reference to FIG. 23. A vacuum chamber 410 is, for example, a processing chamber in a semiconductor fabrication apparatus for performing tasks such as dry etching process or chemical vapor deposition (CVD) process, and is connected to a vacuum pump 412 through an evacuation and exhaust conduit 414. The vacuum pump 412 is used to elevate the pressure of the process gas to an atmospheric pressure so as to evacuate the vacuum chamber 410, and in the past, this role has been served by an oil pump, but lately it has been mainly served by a dry pump. If the degree of vacuum required by the vacuum chamber 410 is higher than that achievable by the dry pump alone, a higher performance vacuum device such as a turbomolecular pump is sometimes used in the upstream side of the dry pump.
The process gas can be toxic or explosive, depending on the nature of the process, and cannot be allowed to escape into the environment without being treated. For this reason, an exhaust gas treatment device 426 is placed downstream of the vacuum pump 412 in which those gaseous components which cannot be released to the environment are treated by being adsorbed, decomposed or absorbed, and only the detoxified gases are released. The evacuation conduit 414 is provided with valves to isolate sections, as necessary.
The conventional arrangement of evacuation systems described above share the following common faults.
1. If the reaction byproducts contain corrosive gases, the vacuum pump may be attacked, thus shortening its service life. For example, when etching silicon-based devices with a typical process gas containing CF.sub.4 and O.sub.2, its exhaust gas contains SiF.sub.4, F.sub.2, CO, CO.sub.2 in addition to the residual CF.sub.4 and O.sub.2. Of these gases, F.sub.2 is particularly strongly corrosive (because fluoride radicals are produced in the process) to the vacuum pump. PA1 2. If the process byproduct contains a gas having a high sublimation temperature, which is exhausted by the vacuum pump, the result is the formation of deposit particles within the vacuum pump to ultimately become a reason for its failure to perform. For example, when etching aluminum-based devices by using a typical process gas containing BCl.sub.3, Cl.sub.2, the vacuum pump must exhaust a reaction byproduct gas AlCl.sub.3, in addition to residual BCl.sub.3 and Cl.sub.2. This gas, AlCl.sub.3, does not decompose in the intake side of the pump because of its low partial pressure, but the partial pressure increases in the pressurized exhaust gas to produce precipitation within the vacuum pump to cause performance problems. Similar problems occur when operating a CVD apparatus, for producing SiN films, that produces byproduct gases (NH.sub.4).sub.2 SiF.sub.6 and NH.sub.4 Cl and the like. PA1 3. Solid particles may be discharged from the processing chamber, which may enter the vacuum pump directly to cause operational problems. For example, in the case of a reduced pressure CVD apparatus based on tetraethyloxysilane (TEOS) process for producing Si films, the process gas containing TEOS and O.sub.2 is used, and various types of alcohols and solid SiO.sub.2 particles are produced. The silicon oxide particles are produced as solids in the reaction, and they impart mechanical damage to the vacuum pump. PA1 4. When the byproduct contains a gas which is reactive at high temperatures, it may react within the vacuum pump to cause operational problems. For example, in a CVD apparatus for producing tungsten films using a typical process gas containing WF.sub.6 and SiH.sub.4, the gaseous byproducts HF and H.sub.2 along with residual WF.sub.6 and SiH.sub.4 gases are exhausted from the processing chamber. As the pressure and temperature within the vacuum pump increase, WF.sub.6 and SiH.sub.4 react with each other to precipitate W particles that cause operational problems for the vacuum pump. PA1 5. The conventional facilities are expensive to operate because the process gases are discarded without being reused. Especially some gases such as SiH.sub.4 are expensive, and it is desirable that they be recycled, however, recycling has not been practiced in the past. Also, in the conventional approach, there are trapped several kinds of gases in one trapping device, and it has been laborious to process the byproducts for separation into various components. PA1 6. The entire voluminous exhaust gas must be processed in the exhaust gas treatment apparatus, which leads to a large-scale operation and a huge capital expenditure, in the first place, and the processing steps become complex and the running cost can be expensive.
Of the various problems listed above, corrosion resistant pumps have been developed to deal with the problems presented in items 1, and the problems outlined in item 2 have been dealt with by raising the operating temperature of the vacuum pump; however, such remedies relate only to the vacuum pump operations, and because the overall system problems have not been addressed, progress has been minimal. There have been no considerations given to the problems outlined in items 5 and 6.